Performance Comparison of Step Skew in Interior and Surface-mount Permanent Magnet Machines

The effect of step skew in output torque and back electromotive force for both interior permanent magnet and surface-mount permanent magnet machines is analyzed for a 12-slot/8-pole combination. The theoretical performance of step skew is compared with the practical motors’ results. It is shown that the loss of output torque due to step skew exceeds the theoretical prediction for an interior permanent magnet machine, whereas the theoretical prediction matches quite well for a surface-mount machine. The performances of both surface-mount and interior permanent magnets are analyzed using 3D-finite element analysis and compared with the theoretical estimation. The simulation shows that the optimum step skew angle is different from the theoretical step skew angle. Finally, the simulation results are validated experimentally for both surface-mount and interior permanent magnet machine.